puzzeled by compression test result

[Rob]

Hello,

I did a compression test today on my 97 mistubishi colt (mirage) 1.3 injection (265 000km) and I’m a bit puzzeled by the results

(PSI / BAR) 1 – 2 – 3 – 4

203/14.0 – 175/12.2 – 175/12.1 – 175/12.2

Factory spec (at 250-400 rpm, I assume my starter can not exceed that) says 12.26 bar by default, min 8,6 or something, and a max difference of 1 bar.

i’m quite puzzled by how the result can be higher. The reason i was preforming this check is because I’m (slowly) losing coolant but can’t find a leak. While testing I figured I could not judge this unexpectedly high first result before testing the other 3 cylinders.
Liquid in the cylinder could raise compression.. and i’ve seen a tiny bit of mist come from a cylinder while testing cylinder 3 or 4. Sadly i wasn’t really considering this possibility yet at this time, and did not think much of it, because it was not constant and really very little.

After doing all 4 cylinders once i went back to cylinder 1 because the result was so strange (did we start it longer, was the hose connection on tighter etc.) but still a result of 200 PSI / 14 bar. Any fluid in there would have been blown out I would think (?).

Or.. this borrowed meter is worthless, and all results are too high. I don’t know if a deviation from factory specification is expected at this mileage (it uses a tiny bit of oil and probably half of that is from leaking). Assuming that in the best case the compression is 12 – 10 – 10- 10. Compression down on 3 cylinders seems unlikely to me (due to a head gasket failure, with slight coolant loss and no clouds of smoke).

Will repeat this check tomorrow, with a cold engine first (today it was fairly warm) and inspect cylinder 1 for fluids. Plugs looked normal and equal. (or as expected really, one is slightly fouled with oil, likely due to a valve stem seal or something. This has been the case with cylinder 1 since i bought the car 3 years ago.

Any suggestions/advice?

Thanks,

Topic

[Rob]

Thanks for the info JC822, I’ve just found and ordered a kit with a UV torch from a little closer to home.

Time for an update on the coolant situation. Tuesday morning, after 3-4 drives and a total of 100 km or so I had to add about 0,5 liter of coolant to the radiator. On my way to work I picked up a new radiator cap, just to rule it out. Situation since does not appears to have changed. When the engine is hot, the coolant is up to the drain of the overflow tank, when the system cools down it does pull back a sizable volume of coolant, but with each drive more air remains in the radiator.

The cap of the expansion tank fits snugly, no signs of leaking anywhere except via the drain/overflow tube behind the bumper, the hose from the radiator to the expansion tank has no signs of wear or anything. Connections at both ends are on so securely it would probably even be fine without the hose clamps. Really don’t belief there is anything wrong at that side of the system.

The coolant UV dye should be here some time next week. Not all that convinced it will help me, but for roughly 25 usd for a small bottle of coolant dye + a led uv torch its worth a shot. Still in doubt what I’ll do in case I still can’t find it, either taking it to a garage, midlock’s chemical reaction tester (to tell me if this air in the system comes from combustion yes or no) or the coolant system pressure tester.

Both tests have their pro’s and con’s, and I don’t like to go to a garage for non-urgent problems. I should be able to figure this out :blush: I think the pressure tester would prove itself to be useful again, on some future car or motorcycle. But given air/gas makes its way in to the pressurized system the chemical test might be a more logic choice in this specific case. I’ll take some time to think about it while waiting for the dye.

[Author]

Replies